1. Field of the Invention
The present invention relates to a magnetic recording medium that has a low level of head wear as well as little head contamination after running.
2. Description of the Related Art
Magnetic recording media have been widely used as sound recording tapes, video tapes, computer tapes, disks, etc. The density of magnetic recording media has been increasing year by year, and the recording wavelength has been decreasing. Moreover, recording systems from analogue systems to digital systems have been studied.
In particular, a magnetic recording medium in which a ferromagnetic metal powder comprising mainly Fe is coated together with a binder on a non-magnetic support currently dominates the field of media for video for broadcasting and data recording because of its excellent cost performance. In drives for video for broadcasting and data recording, higher capacity together with higher speed of the magnetic recording medium relative to the magnetic head, the so-called xe2x80x98higher transfer ratexe2x80x99, are being developed. In order to achieve a higher capacity, it is necessary to increase the recording density, and a magnetic recording medium having excellent electromagnetic conversion characteristics is required. In systems in which a high capacity and a high transfer rate are realized, particularly in VTRs for broadcasting, an expensive head assembly is installed. Since the relative speed between head and tape is high in accordance with the high transfer rate, wear of the magnetic head seriously affects the maintenance and the running costs of the above-mentioned systems, and there is therefore an intense demand for a magnetic recording medium that has a low level of head wear, thereby increasing the head lifespan.
It is an object of the present invention to provide a magnetic recording medium that has a low level of head wear and changes little over time in terms of head contamination and still frame durability. A particular object is to provide an excellent magnetic recording medium for a system in which there is a high relative speed between tape and head and a large area of tape is used per unit time, the magnetic recording medium having low wear of the magnetic head and at the same time little head contamination.
Usually, when an optimum amount of an ester is present on the surface of a magnetic layer to reduce the head wear, the head wear and the head contamination can be kept low, but since the ester on the surface decomposes over time, the head contamination characteristics are often impaired. With regard to means for reducing the head wear, there are known methods such as a method in which the type of an abrasive in the magnetic layer is changed to one having a lower abrasive power or the amount thereof is reduced, a method in which the composition of an oxide film on the ferromagnetic metal powder is adjusted, and a method in which the kneading intensity during preparation of a magnetic liquid is optimized. However, these methods cannot fully meet the above-mentioned demand.
As a result of an intensive investigation by the present inventor in order to solve the mutually contradictory problems of head wear and head contamination, it has been found that the above-mentioned objects can be accomplished by the magnetic recording media below.
(1) A magnetic recording medium comprising a non-magnetic support, and a magnetic layer formed on or above the support, said magnetic layer comprising a ferromagnetic powder, a binder resin, an abrasive, and a fatty acid ester, the fatty acid ester being a fatty acid alkyl ester compound having an acid hydrolysis rate of 0.030 (1/hr) or less, and the abrasive present on the surface of the magnetic layer satisfying the relational expression:
0.01xe2x89xa6H15/H10xe2x89xa60.20
where H10 denotes the number of particles per unit area having a height less than 10 nm (particles/xcexcm2) and H15 denotes the number of particles per unit area having a height equal to or greater than 15 nm (particles/xcexcm2).
(2) The magnetic recording medium according to (1), wherein the fatty acid alkyl ester compound comprises a fatty acid alkyl ester that is represented by the formula below and has a melting point of 15xc2x0 C. or less:
R1COOR2
(in the formula, R1 is a straight-chain, saturated or unsaturated hydrocarbon group, and R2 is a branched, saturated or unsaturated hydrocarbon group).
(3) The magnetic recording medium according to (2), wherein the fatty acid alkyl ester compound comprises a fatty acid alkyl ester that is represented by the formula below and has a melting point of 15xc2x0 C. or less:
R3COOR2
(in the formula, R3 is xe2x80x94(CH2)16CH3, and R2 is a branched, saturated or unsaturated hydrocarbon group).
(4) The magnetic recording medium according to (3), wherein the fatty acid alkyl ester compound is chosen from the group consisting of 2-ethylhexyl stearate, sec-butyl stearate, 2-hexyldecyl stearate, 3-methylbutyl stearate, and 1-methylbutyl stearate.
(5) The magnetic recording medium according to (1), wherein the abrasive is an inorganic nonmagnetic powder.
(6) The magnetic recording medium according to (1), wherein the abrasive is chosen from the group consisting of a metal oxide, a metal carbonate, a metal sulfate, a metal nitride, a metal carbide, and a metal sulfide.
(7) The magnetic recording medium according to (1), wherein the abrasive is chosen from the group consisting of xcex1-alumina with an xcex1-component proportion of 90% to 100%, xcex2-alumina, xcex3-alumina, silicon carbide, chromium oxide, cerium oxide, xcex1-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, barium sulfate, and molybdenum disulfide.
(8) The magnetic recording medium according to (1), wherein the abrasive has an average particle size of 0.05 to 0.4 xcexcm, and contains 1% to 40% of particles having a particle size that is larger than the average particle size by at least 0.1 xcexcm.
(9) The magnetic recording medium according to (1), wherein the ferromagnetic powder is a ferromagnetic metal powder.
(10) The magnetic recording medium according to (1), wherein the binder resin comprises a combination of a vinyl chloride based resin, a polyurethane, and a polyisocyanate.
(11) The magnetic recording medium according to (10), wherein the polyurethane has at least two glass transition temperatures, one thereof being from xe2x88x92250xc2x0 C. to 10xc2x0 C. and the other thereof being from 40xc2x0 C. to 130xc2x0 C.
(12) The magnetic recording medium according to (1), wherein the nonmagnetic support is chosen from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, and polybenzimidazole.
(13) The magnetic recording medium according to (1), wherein it is produced by carrying out a blade treatment using an abrasive tape while transporting the magnetic recording medium.
(14) The magnetic recording medium according to (1), wherein it is produced by carrying out polishing using a diamond powder-studded rotating roll while transporting the magnetic recording medium.
(15) The magnetic recording medium according to (1), wherein the magnetic layer is formed above the support by forming a non-magnetic layer comprising at least a non-magnetic powder and a binder between the magnetic layer and the non-magnetic support.
The above-mentioned objects, other objects, features, and advantages of the invention will become clear from the following description.